Many of today's diesel engines are utilizing a common rail fuel system that relies on a high-pressure pump to achieve the desired injection pressures. As the desired injection pressures increase, it becomes increasingly more important to provide an efficient pump. One factor that has a negative effect on pump efficiency is the unintended leakage of highly pressurized fuel into a low-pressure area or drain. However, as injection pressures become higher, it becomes more difficult to maintain completely sealed interfaces between interacting components, as the higher pressures often cause leakage that would not otherwise have occurred at lower pressures. One factor that may contribute to leakage is the misalignment of interacting components, such as components that seat against one another. As the pressures increase, the degree of misalignment that will result in a leak becomes smaller and smaller, making it increasingly more difficult to mass produce pumps that have such interacting components.
Although modern machinery and manufacturing processes may allow manufacturers to manufacture precision parts that achieve the necessary degrees of alignment, those parts tend to be more expensive than parts that allow for greater tolerances during manufacture. Generally, the more sealing interfaces that are included within a pump that are exposed to high pressures, such as the pressures generated in modern common rail fuel systems, the more precision parts or components will be required. The need for a greater number of precision parts generally leads to an increased overall cost of the pump. Not only does the need for precision parts increase cost, but the need for more parts in general, also often leads to increased cost.
One example of a common rail pump is described in U.S. Pat. No. 5,058,553, issued Oct. 22, 1991 (“the '553 patent”). The pump described in the '553 patent includes a housing and a cylinder fitted in the housing. The housing includes a cam chamber through which a cam shaft extends. The cylinder includes a slide hole that accommodates a plunger that is reciprocatively moved within the slide hole by the cam shaft. The plunger and the slide hole define a plunger chamber in which low-pressure inlet fuel is pressurized. An electromagnetic valve is screwed into the cylinder and serves as a component through which the low-pressure fuel inlet communicates with the plunger chamber. The electromagnetic valve includes a body, an armature, and a valve plug that moves with the armature between an open and a closed position. When the valve plug is in the closed position, it engages a seat on the body to close off the plunger chamber from the low-pressure inlet fuel. To avoid the leakage of high pressure fuel from the plunger chamber into a low pressure area or drain, leakage will likely have to be avoided between the body of the valve and the cylinder, between the valve plug and the corresponding seat on the valve body, and between the plunger and the slide hole. Thus, there are at least three potential leak paths that need to be addressed, most likely through the use of multiple high precision and relatively costly parts.
It would be desirable to provide a high-pressure pump that is able to overcome one or more of the shortcomings described above.